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Neuroanatomy Exam 3


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Function of vestibular system
sense of equilibrium, senses position and movement of the head, contributes to conscious perception of body position in space, functions autonomically through reflexes
Where are vestibular organs located
in labyrinth
Name two types of vestibular organs
otolith organs and semicircular canals
Function of otolith organs
detect force of gravity and tilt of head
Function of semicircular canals
detect head rotation
Membranous labyrinth containing vestibular receptors is embedded in..
temporal bone
surrounded by..
filled by
What are vestibular receptors
hair cells similar to those in cochlea
Name otolith organs
Sacule and utricle
What do saccule and utricle detect
changes of head angle and linear acceleration of the head
sensory epithelium in sacule and utricle
what is orientation of macule in sacule? utricle?
vertical in sacule , horizontal in utricle
Role of crystals of calcium carbonate
hair cells are embedded within macula, cilia embedded in gelatinous cap, tiny crystals encrust surface of cap, as the head is tilted or accelerated, force is exerted on crystals, causes cap to move, this causes cilia to move
one larger cilia, movement of other cilia dtowards or away from kinocilium cause hair cell to depolarize or hyperpolarize
Name three semicircular canals
superior, posterior and horizontal, oriented perpendicular to each other, detect turning movements of head from side to side or nodding
bulge along semicircular canals where hair cells are located
What is the name of cells with hair cells
Where do cilia project
cilia project into gelatinous structure called cupula
What are canals filled with
endolymph, rotational movement causes endolymph to exert force on ampula, ampula bends and either depolarizes or hyperpolarizes
Where do vestibular afferents project to
vestibular nuclei - superior, lateral, medial inferior, some project directly to cerebellum
Where do vestibular nuclei get input from
cerebellum, visual system, somatosensory system (proprioceptors in neck), reticular formation
Where do axons from otolith organs project to
lateral nucleus
Lateral vestibulospinal tract
neurons from lateral nucleus project to alpha and gamma motor neurons in ventral horn of spinal cord, influence muscles that contribute to equilibrium and posture, somatotopic organization
Where do axons from semicircuar canals project to
medial vestibular nucleus
Medial vestibulospinal tract
neurons from medial nucleus synapse on motor neurons that innervate trunk and neck muscles that orient head
Name one of the major ascending projections
to the nuclei of extraocular muscles - occulomotor, trochlear and abducens
Neurons in medial and superior nuclei project via..
medial longitudinal fascicle
What is the function of this pathway
function of this pathway is to help ensure that retinal image is kept stationary when head moves
What is vestibulocerebellum
flocculonodular and vermis
Vestiulo ocular reflex
reflex that keeps vision focused on a particular area in space regardless of how head moves
Name neurons of VOR
primary afferent fibers from semicurcular canals, neurons in vestibular nuclei that project to nuclei of extraocular muscles, motor neurons in these nuclei that innervate the eye muscles
How does VOR work
by sensing rotations of the head and immediately commands a compensatory movement of the eyes in the opposite direction and with the same velocity
Why is VOR important clinically
abnormal VOR in comatose patient - sign of brainstem damage
How do you test VOR in unconscious state
using caloric stimulation
How do problems with vestibular system manifest themselves?
feelng of disequilibrium or vertigo
Symptoms of labyrinth damage
nystagmus, dizziness with vertigo, nausea, abnormal VOR
Menieres disease
episodic attacks of vertigo, hearing loss, tinnitus (ringing), sense of pressure in ear
In the Muller-Lyer Illusion, why do you see one line as smaller than the other when in fact both lines are the same size?
The line with the normal arrowheads is representative of an outside facing corner, reverse arrowheads - inward facing corner, eyes sees lines as the same, brain shrinks outside corner, enlarges inside corner
Which wavelengths correspond to visual light on the electromagnetic spectrum?
400-700 nm
What is the tough connective tissue that forms the eyeball?
What is its function
protection, focusing
Abnormalities of what structure underlie the most common visual problems?
what is astigmatism
curvature of cornea is greater in one direction then another
What structure focuses light onto the retina? Which muscles control this structure?
lens, ciliary muscles
What is accommodation?
bringing into focus objects from various distances by adjusting lens with muscle
What structure alters the amount of light entering the eye? Which muscles control this structure?
Dilation of this structure occurs via what pathways from what brain structure? Contraction of this structure occurs via what pathways?
constriction - pupillary constrictor muscles which receive parasympathetic information from occulomotor nerve, dilation via pupillary dilator muscle that receives sympathetic innervation from superior cervical ganglia
Where is aqueous humor found?
anterior chamber in front of lens
Where is vitreous humor found?
posterior chamber behind lens
How many eye muscles control eye movement?
three pairs of extraocular muscles
What are the names of these muscles?
medial rectus, lateral rectus, superior rectus, inferior rectus, superior olique, inferior oblique
Why do you have a blind spot?
blind spot is where optic nerve leaves eye

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